Fix: Move Line Up/Down collapses inline editor when moving past the start/end

This is a possible fix for the issue adobe/brackets#1933.

When moving a line down on an inline editor, the problem seems to be moving the line to the last line and not moving the last line beyond the inline widget. But moving the line beyond the inline widgets breaks `getLastVisibleLine()` which starts giving 1 line less than it should and then breaking the move line up.

So this change doesn't move down in an inline editor when trying to move the line to the last visible line or when moving the last visible line down.